Nuclear receptors (NRs) are ligand-dependent transcription factors that regulate the expression of a wide variety of genes involved in nearly al aspects of human physiology and disease. They do so in large part by first binding specific DNA response elements (RE) in regulatory regions of genes. While the past 25+ years has led to a basic understanding of NR DNA binding, recent studies indicate that we have much more to learn about the NR-DNA interaction, and the factors that influence it. Furthermore, while NRs have been investigated heavily for their role in physiology and disease and are themselves targets of many successful drugs, we still do not have a complete understanding of their role in disease susceptibility nor in individual responses to drug treatments. Variability between individuals is determined at least partially by their genetic make-up and single nucleotide polymorphisms (SNPs) are thought to account for much that variability. While many SNPs in the coding portion of genes have been associated with altered protein function, recent genome-wide studies show that certain SNPs are associated with changes in levels of expression of nearby genes (eSNPs). However, what is lacking is a systematic, functional characterization of eSNPs. We propose that a significant proportion SNPs affect gene expression by altering the affinity of NRs for their DNA response elements. In this proposal, we will examine NR DNA binding specificity and how it is influenced by SNPs by integrating a range of biochemical, molecular, genomic and bioinformatics approaches in three Specific Aims: In Aim 1, we will exhaustively determine the DNA binding specificity of a select group of NRs using an integrated approach based on protein binding microarrays (PBMs). PBMs are a novel, high throughput (10- 100,000's reactions) in vitro DNA binding assay. The PBM results will be used to search the genome for potential NR target genes and then cross referenced with genome-wide location and expression analysis. In Aim 2, we will expand PBMs to 1 million reactions in order to identify affinity altering SNPs (aaSNPs) for NRs in regulatory regions of genes associated with disease and drug metabolism. The results from the SNP PBMs will be cross referenced with publicly available databases (GWAS, dbSNP, GTEx, etc.) in order identify aaSNPs that have effects on expression levels of genes relevant to disease and drug metabolism. In Aim 3, PBMs will be used to investigate the effect of a variety of factors on NR DNA binding, including different ligands, NR partners, co-regulatory molecules. All results will be made publically available on a website dedicated to the project, as well as other public databases, and web-based tools for motif finding and target gene prediction will be developed. They will advance the long term goal of fast tracking research linking NRs to disease and drug metabolism, and thereby help personalize medicine and ensure that drugs that target NRs can be used in a more effective fashion.